Yeah you can't recruit tier 5 and above units. Not sure if it's intended
Yeah I like that idea if I could put focus points into my companions more reliably and their trade would actually rank up.
Just simply slowing them down would eat their profits up too because they're slower walking from town to town as well as make them more vulnerable.
One thing to add which I just thought of is that caravans don't really give you much in the form of wealth when you attack them as the player. You get more wealth off of prisoners and armour/weapons than actual trade goods.
You could also add an insurance system to protect against any unforeseen circumstances but eat into your profits.
Pretty sure I've seen greater relation increases than that and seen quests disappear when they enter a village.
As mentioned above it takes 30hours on the campaign map alone excluding any other activity for 50 in game years to pass. You can conquer the whole map twice over in 30 hours.